1. Field of the Invention
The present invention relates generally to the field of processor-based imaging, and, more particularly, to invisible space skipping with adaptive granularity for texture-based volume rendering.
2. Description of the Related Art
Texture-based volume rendering has recently become the most popular volume rendering technique due to its performance advantage over software-based approaches (e.g., ray casting), and due to its cost advantage over customized hardware (e.g., VolumePro™). Volume rendering is notorious for being very computationally intensive. Even with modem graphics hardware, there is a desire, and indeed a need, to process relatively large datasets faster for standard texture-based volume rendering. Furthermore, the problem is compounded with the continual increase in the size of volume datasets.
Various approaches have been used to accelerate volume rendering (without compromising image quality) by ignoring portions of the volume that will not contribute to the resultant image. Li et al., Accelerating Volume Rendering with Texture Hulls, “IEEE/SIGGRAPH Symposium on Volume Visualization and Graphics”, Boston, Mass., October 2002, pp. 115-122, Li et al., Empty Space Skipping and Occlusion Clipping for Texture-based Volume Rendering, “IEEE Visualization”, December 2003, pp. 317-324, and Li et al. Texture Partitioning and Packing for Accelerating Texture-based Volume Rendering, “Graphics Interface”, Halifax, Canada, 2003, pp. 81-88, the disclosures of which are fully incorporated by reference herein, decompose a volumetric dataset into sub-volumes during preprocessing to later facilitate skipping sub-volumes that are either completely transparent or completely occluded. These approaches all use a flat single-level geometric description of empty space. Other researchers have used hierarchical structures to skip empty space. Empty space has been based solely on voxels that are mapped to complete transparency by the transfer function.